Describe the bug

• U+25C8 (White Diamond Containing Black Small Diamond) is missing.
• U+25C9 (Fisheye) is weird in Libertinus Serif Bold, with an offset central dot and a bigger size.
• The shapes of several of these characters are inconsistent in the Serif Italic / Sans Italic fonts.

Expected vs. actual behavior

• The three diamonds (U+25C6, U+25C7, U+25C8) are sometimes used in dictionaries, for instance, to denote synonyms, antonyms or related words. They are very simple shapes, so there's no reason for not having U+25C8 (see below)
• U+25C9 in Libertinus Serif Bold should have the central circle properly centered
• On italic vs. non-italic, I don't know what would be expected for these shapes, but see screenshot below, it's not consistent currently, and not very logical

Screenshots / logs

Regarding U+25C8

It wouldn't be hard to add it, e.g. I tried the following addition to LibertinusSerif-Regular.sfd...

StartChar: uni25C8
Encoding: 9672 9672 2731
Width: 666
GlyphClass: 2
Flags: MW
LayerCount: 2
Fore
SplineSet
195.85 214.65 m 1
 332.65 351.45 l 1
 469.45 214.65 l 1
 332.65 77.85 l 1
 195.85 214.65 l 1
EndSplineSet
Refer: 1846 9671 N 1 0 0 1 0 0 2
EndChar

It would look quite correct...

For the other characters, see below:

• U+25C9 is weird in Libertinus Serif Bold, as mentioned
• For other characters in the Italic styles, they are sometimes slanted, sometimes not.